Next time you have a chance to watch someone reading a map, look for the first thing they do. They'll likely do the exact same thing everyone else does: find themselves on the map.
It doesn't matter what kind of map it is, whether it's of their neighborhood or an amusement park. They'll open the map and find something that is personally meaningful, such as their house or their favorite roller coaster.
Psychologists call this 'grounding'—the natural behavior of initially finding a known reference point in a foreign information space. Once the person has grounded themselves, they can then use the starting point to understand the rest of the space.
While grounding helps people adjust to complex situations, it can be detrimental when it happens during the design process. If, while conjuring up an interface, designers ground themselves in the design, they run the serious risk of creating an interface that only they can use.